Butyl Rubber Flame Retardancy for Cable Insulation

Overview of Technical Issues:

The butyl rubber insulating material structure insufficiently blocks flame propagation when exposed to ignition sources, allowing continued combustion that degrades the insulation barrier and creates fire hazards in cable systems; the goal is to optimize the flame retardancy performance to meet cable safety standards while maintaining the electrical insulation and mechanical properties required for reliable cable operation.

Solution directions generated for this problem

Problem Direction 1 :

ImproveHeat absorption capacity during pyrolysis
VS
ConstraintMaterial mechanical flexibility

Inspiration 1 : Cross-domain reference

Application Principle: #31 Porous materials
Cross-domain applicability Assess applicability
A method for preparing porous metallic iron
Innovative Solution Refine solution

Microencapsulated metal hydroxide foam structure for flexible heat-absorbing insulation

Introduce cellular foam architecture in butyl rubber matrix
How to solve :
  • Microencapsulate aluminum hydroxide (Al(OH)₃) particles in 5-15 μm diameter capsules with silicone shell, load at 45-50 wt% into butyl rubber
  • inject supercritical CO₂ at 10-15 MPa and 160°C during extrusion to create uniform closed-cell foam with 20-30% porosity and 50-150 μm cell size
  • cellular geometry distributes filler stress across cell walls, maintaining elongation ≥280% while achieving 320 J/g endothermic capacity to reduce flame temperature below 300°C through Al(OH)₃ dehydration at 220-350°C
Expected Effect : Elongation ≥280%, flame temp <300°C, heat absorption 320 J/g, porosity 20-30%
Risk Control :
  • cell size uniformity control (CV<15%)
  • capsule shell integrity during foaming
  • foam collapse under cable bending cycles

Problem Direction 2 :

ImproveChar layer formation rate
VS
ConstraintManufacturing processability

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
Metal oxide film and semiconductor device
Innovative Solution Refine solution

Pre-crosslinked char-former oligomer system for rapid barrier formation

Pre-synthesize char oligomers before compounding
How to solve :
  • Pre-polymerize phosphorus-nitrogen char precursors into stable oligomers (Mw 800-1500 Da) at 120-140°C for 2-4 hours before mixing with butyl rubber, converting reactive monomers into thermally-stable species that remain inert during extrusion
  • Compound pre-formed oligomers at 25-35 wt% loading into butyl rubber matrix via twin-screw extrusion at 160-175°C, maintaining melt flow index above 8 g/10min to preserve standard processing cycle time
  • Upon flame exposure above 280°C, oligomer terminal groups rapidly cross-link within 15-18 seconds forming dense char network, while encapsulated expandable graphite (5-8 wt%, expansion onset 220°C) synergistically reinforces barrier structure to achieve below 18% porosity
Expected Effect : Char formation time reduced to 15-18s; extrusion viscosity increase limited to 10-15%; barrier porosity below 18%; elongation maintained above 280%
Risk Control :
  • oligomer molecular weight distribution control
  • thermal stability verification at processing temperature
  • char layer adhesion to substrate interface

Problem Direction 3 :

ImproveFlame-blocking barrier structural density
VS
ConstraintMaterial mechanical flexibility

Inspiration 1 : Cross-domain reference

Application Principle: #40 Composite materials
Cross-domain applicability Assess applicability
Abrasive particles having complex shapes and methods of forming same
Innovative Solution Refine solution

Dual-phase butyl rubber composite with gradient intumescent microsphere distribution

Composite structure with gradient microsphere distribution
How to solve :
  • Formulate dual-phase composite: outer layer (1.5mm) contains 55% spherical intumescent microspheres (expandable graphite core + APP shell, 80-120μm diameter) to form dense char barrier with porosity <15%
  • inner layer uses pure butyl rubber maintaining elongation ≥320%
  • Establish gradient transition zone (0.8mm) between layers with microsphere concentration decreasing from 55% to 5% via co-extrusion with controlled feed rate ratio 3:1, ensuring interfacial bonding strength ≥8 MPa through partial crosslinking at 165°C
  • Control microsphere sphericity ≥0.92 (measured by dynamic image analysis) to minimize stress concentration
  • extrusion temperature 160-175°C, screw speed 45-60 rpm, die pressure <12 MPa to prevent premature expansion
Expected Effect : Char porosity <12%, elongation 310-340%, extrusion cycle +8%
Risk Control :
  • microsphere size distribution deviation ±15μm
  • layer interface delamination under bending
  • premature microsphere activation during processing

Problem Direction 4 :

ImproveFlame-blocking barrier structural density
VS
ConstraintManufacturing processability

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Mechanism of urea/solid acid interaction under storage conditions and storage stable solid compositions comprising urea and acid
Innovative Solution Refine solution

Thermally-activated liquid char former for dense barrier formation

Use liquid-phase char formers that remain low-viscosity during extrusion but solidify into dense barriers at ignition
How to solve :
  • Replace 40-50% solid char-forming fillers with reactive phosphate ester liquids (e.g., resorcinol bis(diphenyl phosphate)) that plasticize butyl rubber at 160-180°C extrusion temperature, maintaining melt flow index ≥8 g/10min
  • Upon flame exposure above 300°C, liquid phosphates undergo rapid polymerization and cross-linking within 15-20 seconds, forming dense char network with porosity below 12% through phosphorus-carbon bond formation
  • Incorporate 10-15% expandable graphite (expansion ratio 200:1 at 280°C) as synergist to fill residual pores, achieving final barrier density with air void fraction under 10% while maintaining extrusion cycle time within baseline ±5%
Expected Effect : Barrier porosity reduced to 10%, extrusion time unchanged, elongation retained at 280%
Risk Control :
  • liquid phosphate migration during storage
  • graphite expansion timing mismatch
  • char layer adhesion to substrate insufficient
Patsnap Eureka Solution